Poly-meta-phenylene isophthalamides



Nov. 22, 1966 w. SWEENY POLY-META-PHENYLENE ISO-PHTHALAMIDES v 2Sheets-Sheet 1 Filed May '7, 1965 FIGJIa ATTORNEY Nov. 22, 1966 FiledMay 7, 1965 W. SWEENY 2 Sheets-Sheet 2 ACID CHLORIDE DIAMINE SOURCESOURCE COOLER MIXER HEAT EXCHANGER cqwm souncz NEUTRALIZER BLENDING mmmums mm DEAERATOR FILTER POLYMER STORAGE FIGY INVENTOR WILFRED SWEENEYATTORNEY United States Patent M 3,287,324 POLY-META-PIENYLENEISOPHTHALAMIDES Wilfred Sweeny, Wilmington, DeL, assignor to E. I. duPont de Nemonrs and Company, Wilmington, Del, a

corporation of Delaware Filed May 7, 1965, Ser. No. 454,086 9 Claims.(Cl. 260-78) This application is a continuation-in-part of applicationSerial No. 171,755 filed February 19, 1962, which is acontinuation-impart of Serial No. 774,156, filed November 17, 1958 (nowPatent No. 3,094,511 dated June 18, 1963), which in turn is acontinuation-in-part of Serial No, 642,928, filed February 28, 1957, andnow abandoned.

This invention relates to a novel and useful synthetic textile fiber andfabrics produced therefrom. More specifically it rel-ates to a textilefiber from poly(m-phenyleneisophthalamide) and ring substitutedderivatives thereof, hereinafter referred to as MPD-I polymers.

Textile fibers from synthetic polymers are conventionally prepared byextrusion of a melt (melt spinning) or a solution (dry spinning) of thepolymer. A relatively low melting point or high solubility of polymer istherefore conducive to ease of fiber formation. These same properties,i.e., low melting point and high solubility, are however highlyundesirable in a textile material for obvious reasons. The presentinvention provides a class of synthetic, fiber-forming polymers whichare capable of existing in two forms, one form, referred to hereinafteras the alpha form (i.e., a-MPD-I polymers), having high solubility, theother, referred to hereinafter as the beta form (i.e., B-MPD-Ipolymers), possessing low solubility.

It is an object of the present invention to provide polymers of oz-MPD-Iand G-MPD-I of fiber-forming molecular weight.

Another object is to provide a useful shaped structure from aand B-MPD-Ipolymers.

Another object is to provide a process for forming a synthetic textileof fi-MPD-I polymers from a textile of oc-MPD-I polymers.

A further object is to provide a synthetic textile fiber having a highflame resistance.

These and other objects will become apparent in the followingspecification and claims.

The present invention provides the novel and useful polymers of a-MPD-Iand fi-MPD-I, shaped structures thereof and processes for theirproduction. In accordance with the present invention, polycarbonamide isprovided having an inherent viscosity of at least 0.8 in sulfuric acidat 30 C. at a concentration of 0.5 gram of polymer per 100 cc. ofsolution, the polycarbonamide of the class consisting of (a) an alphapolymetaphenylene isophthalamide characterized by relatively highsolubility and (b) a beta polymetaphenylene isophthalamide characterizedby relatively low solubility, the polycarbonamide consisting ofrepeating units of which at least about 85% are of the formula R H H 0 Il l II II N NC R- R R- R wherein the hexagon represents the benzenenucleus, R is a non-amide forming substituent on nuclear carbon.Preferably at least two or three of the R groups are hydrogen, andcopolymeric units, when present, are carbonamidic.

By a non-amide forming substituent is meant a substituent which isnon-amide forming at room temperature PatentedNov. 22, 1966 via reactionwith a member from the class consisting of amino hydrogen and carbonylhalide.

The invention will be more readily understood by reference to theillustrations.

FIGURE I is an X-ray diffraction pattern of the amorphous form of anMPD-I polymer. FIGURES II, III and IV are X-ray diffraction patterns ofthe crystalline form of MPD-I polymers in the 0:, B and salt complexforms respectively. FIGURES Ila, Illa and Na being artistsrepresentations of each of the respective corresponding photographicimages. FIGURE V is a flow sheet of the continuous process referred toin Example 16.

MPD-I polymers, as defined above, are characterized by the existence oftwo linear forms which will be referred to hereinafter as an alpha(soluble in selected organic solvents) form and a beta (insoluble inorganic solvents) form. As will be further explained hereinafter, eachof the uand ,B-forms may be complexed using selected salts as describedhereinafter to render the 5- form soluble in organic solvents and toincrease the solubility of the u-form. MPD-I polymer may also exist inthe cross-linked form, i.e., intractable and insoluble in concentratedsulfuric acid as well as organic solvents. In each of the alpha form andthe beta form the polymer or shaped structure formed therefrom may existin the amorphous or the crystalline state. The alpha form of polymer canbe formed by low temperature polymerization. Attempts to obtainfiber-forming molecular weight by high temperature polymerization astaught in US. 2,244,192 always lead to formation of cross-linked polymerwhich cannot be employed to form shaped articles. The alpha form ishighly soluble in conventional dry spinning solvents such asdimethylformamide and dirnethyl acetarnide, Whether in the amorphous orcrystalline state. The beta form is insoluble in such solvents whetherin the amorphous or crystalline state. While applicants do not Wish tobe bound by any theory of operation, it is believed that a network ofinterchain hydrogen bonding, which may be ordered enough to becrystalline, between the carbonyl oxygens and weakly acidic -NH groupsof adjacent chains, is characteristic of the beta form. On the otherhand, the alpha form of the polymer is largely free of such bondings dueto intrachain hydrogen bonding between carbonyl oxygens and weaklyacidic NH groups of another recur-ring unit in the same chain. Thus thealpha form of the polymer is characterized by a hydrogen bonding whichmay be represented by a folded or coiled structure as follows:

the paired dots in the formula indicating hydrogen bonding and thesymbol R representing phenylene or substituted phenylene upon which thecarbonyl and amine substituent groups shown are meta oriented. The highdegree of intrachain hydrogen bonding obtained is believed possible dueto the short distance between adjacent carbonyl and imine groupspeculiar to the meta orienta- 3 tion of each group. This bonding permitsa high degree of solubility as compared with structures having asignificant amount of the beta form which beta form may be representedas follows:

The alpha form may be converted to the beta form by (a) increasing thechain mobility with heat, suitable plasticizers or solvents so that thechain can rearrange to the more stable ,B-structure (this is acceleratedby the presence of H-bond active material such as water, alcohol orcarboxylic acids) and (b) by ordering the chain molecules by someprocess of orientation, as in the shearing of a solution, casting of afilm, spinning a fiber or drawing a yarn. The alpha form in solution isconverted to the beta form slowly at room temperatures but more rapidlyat higher temperatures. Such conversion in solution is normallyundesirable since the solutions gel to immobility. It is thereforeconvenient to convert the alpha to the beta form during the spinning orcasting operation in the formation of shaped objects such as fibers orfilms. The temperature at which conversion from the a to the t3 formoccurs in solution will vary depending upon the nature of the solvent(due to differences in solvent power). Thus the oc form is relativelystable in dimethylforrnamide at from about l C. to about +15 (3.,whereas in dimethylacetamide the range of solution stability shifts tofrom about 0 C. to about 35 C. In dry N-methylpyrrolidone, the a form isrelatively stable from room temperature to about 80 C. Conversion fromthe a to the 6 form can occur rapidly as will be demonstrated belowwhere a film of soluble a polymer is rendered insoluble by being plungedinto the same solvent at elevated temperature.

It will be obvious from the above discussion that useful shapedstructures such as fibers and films cannot be made from cross-linkedMPDI due to its intractable and insoluble nature. On the other hand, thea form is readily extruded or cast into fibers and films due to itssoluble nature. The structures formed are particularly valuable sincethey may be converted after shaping into the ,B or even the intractablecross-linked form. It will also be obvious, as is demonstrated below,that preparation of the a form of polymer must be by a low temperatu-retechnique, since melt polymerization leads to the cross-linked variety,when attempt is made to polymerize to a fiber-forming molecular weight.

The following examples are intended to illustrate the invention. Theyare not intended to limit it in any manner. All parts and percentagesare by weight unless otherwise indicated. Values of inherent viscosityare determined in sulfuric acid (sp. gr. 1.841 at 60 F.), at 30 C. at aconcentration of 0.5 gram polymer per 100 cc. of solution. All polymersof this invention have an inherent viscosity of at least about 0.8 onthis basis (i.e., they are of fiber-forming molecular weight) and apolymer melt temperature of at least about 300 C. (When a powdered,high-melting-point polymer is placed at the proper point on a meltingbar which is heated at one end only so as to provide a suitable gradientin temperature along its length, the polymer will generally be observedto soften to a plastic, deformable mass which may stick to the bar.

This softening point is what is intended by the expression polymer melttemperature. Measurement of surface temperature of the bar at the pointof softening and sticking provides a reasonably reproducible indicationof melting point. The higher this temperature the greater the error inthe measurement and the more subjective it becomes.) Unsymmetricalsubstituents such as that disclosed in Example 10 reduce the polymermelt temperature somewhat, but not below 300 C. Some ring substitutions,as for example, that disclosed in Example 11 actually increase thepolymer melt temperature over that of the polymers made from aromaticdiamines and diacyl halides Without ring substitnents.

Example 1 A solution of 10.3 grams of isophthaloyl chloride and one dropof sulfuric acid in 175 ml. of tetrahydrofuran is added at roomtemperature to a rapidly stirred solution of 5.4 grams of m-phenylenediamine and 10.6 grams of sodium carbonate in 150 ml. of water. Afterstirring for five minutes, the polymer formed is collected on a filter,washed in a blender twice with Water and twice with acetone andthereafter dried at room temperature under vacuum. The inherentviscosity of the product is 2.1. This is the 05 form of polymer as isevidenced by its solubility in dimethylformamide at 0 C. and in eitherdirnethylacetami-de or N-methylpyrrolidone at room temperature to theextent of .at least about 5%. The product has a polymer melt temperatureof 360 C.

Example 2 A shaped amorphous structure of the or MPDI is prepared bycasting a film of a solution of two grams of the above prepared polymerin 13.4 grams N-methylpyrrolidone under cyclohexane, carefully excludingmoisture. After hardening under the liquid for 20 minutes the film isdried for 18 hours in a vacuum oven at 50 C. with a stream of drynitrogen blowing through it. The dried film can be redissolved indimethylformamide at 0 C. and in either dimethylacetamide orN-methylpyrrolidone at room temperature. An X-ray diffraction pattern ofthe amorphous film is shown in FIGURE I. When ether is substituted forcyclohexane in the above procedure, the resulting film is also solublein dimethylformamide, dimethylacetamide and N-methylpyrrolidone, asexpressed in Example 1, but shows a trace of oz crystallinity in itsX-ray pattern.

Example 3 A shaped highly crystalline structure of the a MPD-I isprepared by casting a 6 in. by 2 in. film from a solution as employed inExample 2, in air and at room temperature and with exclusion ofmoisture. The resulting film is immediately placed in a vacuum oven andis dried at room temperature with a gentle stream of dry nitrogenpassing over it for 60 hours. The resulting film is opaque, tough andsoluble in dimethylformamide at 0 (3., dimethylacetamide at 25 C. andN-methylpyrrolidone at C. Its X-ray diffraction pattern, FIGURE H,demonstrates that it is highly crystalline.

Example 4 A shaped structure having medium crystallinity of the B MPD-Iis prepared by modifying the procedure of Example 3 above by drying thefilm at room temperature in air. This film is insoluble in all of thesolvents listed under Example 3 except the N-methylpyrrolidone at 80 C.

Example 5 A portion of the shaped highly crystalline structure of 0cMPDI prepared in Example 3 is converted to a highly crystalline B MPD-Iby plunging the film in dimethylformamide heated to about C. and keepingit at this temperature for about 2 hours. Transformation from the a tothe 5 form is so rapid that no visible solution of the a form occurs.The resulting film is there- Example 6 fection of crystallinity is alsoindicated in the table. The

solubility was determined in dimethylformamide at C.

TABLE I Crystallinity Sample Temp., O. Solubility Amount Perfection 180Swells Medium 214 Insoluble While Examples 1-6 above show thepreparation of films for illustrative purposes, it will be obvious tothose skilled in the art that other shaped structures such as fibers,coated and molded articles and the like may also be formed from the onform of the polymer by conventional techniques, due to the solubility ofthis form of polymer. Because the alpha-form is rapidly converted to thebeta-form by heat, spinning of fibers from the alpha-form may best beaccomplished in a wet-spinning process wherein low solution temperaturesare consistent with practical spinning rates. Thereafter the structurein the shape desired may be transformed into the ,8 form to render itinsoluble in solvents such as dimethylformamide, dimethylacetamide andN-methylpyrrolidone. More conveniently the transformation from on to 5form may take place during or in conjunction with the shaping operation.For instance, in the formation of fiber, the a form may be wet spun andconverted to the 3 form in a subsequent wet extraction-heatingtreatment.

The preferred method of forming structures of B polymer from the atpolymer involves the use of a salt complex which renders the polymermore soluble and stabilize the solution by inhibiting or retarding the ato {3 transformation by preventing the inter-chain hydrogen bondingwhich is responsible for the beta form. Solutions using such complexesare described and claimed in Beste and Stephens, United States Patent3,068,188 issued 12/11/62. While applicants do not wish to be bound byany particular theory, it is postulated that the selected salts havegreater attraction for the amide groups than the amide groups possessfor each other. Thus when the hydrogen bonding of the a form isdisturbed, for instance, by increased chain mobility or ordering of thechain molecules, formation of the salt complex is favored overinterchain bonding which would lead to the ,8 form, thus maintaining thepolymer in a non-hydrogen bonded condition. The salt complexintermediate technique permits the polymer to be handled at a highertemperature than is possible without complexing. The salt isconveniently removed from the shaped structure by aqueous boil-off,which also serves to transform the shaped structure into the {3 form.Obviously prolonged heating or heating at a high temperature may beemployed to transform the shaped structure into the truly cross-linkedcondition. The examples below illustrate the technique of forming ashaped structure wherein the intermediate salt complex form is involved.

Example 7 (A) Meta-phenylenediamine dihydrochloride in the amount of 5.4parts is placed in a reaction vessel fitted with a high speed stirrerand a solution of 12.1 parts of triethylamine in 200 parts methylenechloride is added rapidly. The mixture is stirred for one minute todissolve the diamine salt. Triethylamine hydrochloride is formed insitu. 6.1 parts of isophthaloyl chloride in 200 parts of methylenechloride are then added. Polymerization is completed and a MPD-I isprecipitated by addition of a volume of hexane about equal to the volumeof the reaction mass. The product is water-white and has an inherentviscosity of 1.71. It is obtained in 91% yield.

A blend of several polymers in the or form prepared by the procedureoutlined above is dissolved to a concentration of 17% in a mixture of 95parts dimethylformamide and 5 parts lithium chloride. This solution at128 C. is spun through a 5-hole spinneret, in which each orifice has adiameter of 0.10 mm., into an air column maintained at 225 C. Fiber,wound up at the rate of 92 yards per minute is thereafter drawn to 4.00times its original length and boiled off in water to remove the salt.The final fiber, 8 MPD-I, has a tenacity of 3.8 grams per denier, with a39% elongation at the break.

(B) Another sample of the same polymer is dissolved in a mixture of 95%dimethylformamide and 5% lithium chloride to give a 15% polymersolution. This solution is cast into a film. The solvent is flashed offin an oven at C. The resulting film is leached in water at 65 C. for 24hours to remove residual dimethylformamide and salt. Test strips of thewet film of ,8 MPD-I so formed are clamped in frames prior to drying ina vacuum at 90 C. Physical properties of the films at varioustemperatures are reported in the table below:

TABLE II Tensile Modulus Percent Temperature, 0. Strength (p.s.i.)Elongation (p.s.1.)

The film is also noted to have a high dielectric constant which dropsoff only fractionally at temperatures as high as 200 C., whilecommercially available insulating materials such as polyethylene orrubber are either completely destroyed or become molten at suchtemperatures.

(C) In order to illustrate the non-flammable nature of the polymers,another sample of fiber similar to that prepared in paragraph (A) ofthis example (differing only in that it was drawn X 4.75 and had 4.9gms. per denier tenacity and 30% elongation at the break) is subjectedto a standard flammability test (A.A.T.C.C. 45 angle test, AmericanHandbook of Synthetic Textiles, 1st Ed. 2), Textile Book Publishers Inc,NY.) along with a cotton fiber control. Both fibers are knit into tubesand exposed to an open flame until ignited, at which time the flame isremoved. Test results are shown in the table below:

TABLE III.FLAMMABILITY OF KNIT FAB RIOS Sample Ignition Total Time toBurn Dimensions Char Type of Burning Type of Time, sec. Zone (inches)Residue Test Fiber (five samples) 3. 8 Went out (5.4 sec.) 0.35 x 0.30Slow ignition, negligible burning period Crusty hard.

Cotton fiber (five samples). 2 13 to 430 secs 1.5 x 6, sample burnedcompletely.

Rapid ignition, quick flaming, glowing Feather.

char slowly disintegrates.

As can be seen, the fiber of this invention is outstandingly superior tocotton in flame resistance. In similar tests, the fibers of thisinvention are compared to other commercial synthetic fibers, and provedmore difiicult to ignite and in addition were self-extinguishing. Asample of a fabric from poly(hexamethylene adipamide) yarn is burned tothe extent of of the fabric area, while the fabric prepared from fibersof this example is charred for less than A of its area.

(D) In another typical preparation of MPD-I, a solution of 2.0 grams ofisophthaloyl chloride in 2.00 cc. of methylene chloride is added to astirred and cooled (ice) solution of 1.8 grams of m-phenylenediaminedihydrochloride and 4.1 grams triethylamine in 50 cc. of methylenechloride. The polymer precipitates immediately. Stirring is continuedfor 10 minutes after which the polymer is filtered, washed with warmwater and dried at 60 C. under vacuum. A yield of 1.5 grams of polymerhaving a polymer melt temperature estimated at about 360 C. and aninherent viscosity in dimethylformamide of 1.06 is obtained. A film iscast from a solution of the polymer in dimethylformamide. After the filmis dried at 90 C. it is observed to be no longer soluble indimethylformamide.

The or form of the polymer from which the fiber or other shapedstructure is produced is formed by a low temperature, solventpolymerization technique as illustrated in the specific examples. Theprocess is described in greater detail and claimed in copending U.S.P.3,063,966, issued 11/11/62 to Kwolek, Morgan and Sorensou filed February5, 1958. In general the process comprises combining the diacid halide ofisophthalic acid with m-phenylenediamine in the presence of an acidacceptor in a liquid reaction medium which is a solvent for eachreactant such as chloroform, methylene chloride, 1,1,2-trichloroethane,1,2-dichloroethane, methyl ethyl ketone, acetonitrile, tetramethylenesulfone, 2,4-dimethyltetramethylene sulfone, diethylcyanamide,dimethylcyanamide, chlorobromomethane, symtetrachloroethane, cis-1,2-dichloroethane, propionitriie, N-rnethyl pyrrolidone and the like.Suitable acid acceptors include trimethylamine, triethylamine,ethylpiperidine, diethylbenzylamine, dimethylbenzylamine,ethylmorpholine, methylmorpholine,N,N,N',N-tetramethylhexamethylenediamine and the like as well as amidetype materials which may also serve simultaneously as a liquid reactionmedium.

The MPD-I polymers of the present invention consist of at least about85% repeating polycarbonamide units of the formula preferably members ofthe class consisting of lower alkyl, lower alkoxy, halogen, nitro,cyano, sulfonyl, lower carbalkoxy and hydrogen. Other aromatic as wellas aliphatic cycloaliphatic and heterocyclic diamines may be employed ascopolymeric components Within the limits set forth above. Typicalcopolymer forming reactants include single, multiple and fused ringaromatic diamines, in which the amino groups are oriented ortho, meta orpara with respect to each other as 4,4-oxydiphenyldiamine, 4,4sulfonyldiphenyldiamine, 4,4 diphenyldiamine, 3,3-diplienyldiamine;aliphatic, cycloaliphatic and heterocyclic diamines as ethylene diamine,hexamethylene diamine, diaminocyclohexane, piperazine and the like; andthe compounds corresponding to any of the above in which one or morehydrogens are replaced by lower alkyl, lower alkoxy halogen, nitro,sulfonyl and low carbalkoxy groups as Well as metaand paraphenylenediamines bearing such substituents for hydrogen. Copolymers may also beformed wherein the diacid compound is other than isophthalic acid.Suitable acids for use in preparing such copolymers include aromatic,aliphatic, cycloaliphatic and heterocyclic compunds. Specific typicalacids are single and multiple and fused ring aromatic acids, in whichthe acid groups are oriented ortho, meta or para with respect to eachother such as terephthalic acid, 4,4'-oxydibenzoic acid,4,4-sulf0nyldibenzoic acid, 4,4-dibenzoic acid, 3,3- oxydibenzoic acid,3,3-sulfonyldibenzoic acid and 3,3- dibenzoic acid; aliphatic acids suchas adipie, sebacic, azelaic and the like, and compounds corresponding toany of the above in which one or more hydrogens are replaced by one or acombination of lower alkyl, lower alkoxy, halogen, nitro, sulfo, lowercarbalkoxy groups. Such copolymeric units are particularly valuable inrendering the fiber sensitive to particular dyes. Examples 8 to 12 belowillustrate various substituted MPD-I polymers and also copolymers.

Example 8 Fiber-forming poly(meta-phenylene chloroisophthalamide) ofhigh polymer melt temperature is prepared using methylene chloride asthe reaction medium, in the presence of triethylamine as acid acceptorand in the presence of excess of triethylamine hydrochloride. Inpreparing the polymer, 7.12 parts of 4-chloroisophthaloyl chloride in143 parts of methylene chloride is added to a Waring Blendor containing5.43 parts of metaphenylene diamine dihydrochloride, 12.14 parts oftriethylamine and 143 parts of methylene chloride. After stirring for 10minutes, the alpha polymer having an inherent viscosity of 0.84 isobtained.

Example 9 A nuclear substituted aromatic polyamide of high molecularweight and high polymer melt temperature, the nuclear substituents beinglower alkyl or lower alkoxy, can be prepared in the same reaction mediumand under the same conditions as the unsubstituted polymer. Forinstance, methylene chloride using triethylamine as an acid acceptor andin the presence of 50% excess triethylamine hydrochloride is suitablefor the preparation of ply(4-rnethy1 meta-phenylene isophthalamide),since the same system is suitable for poly(meta-phenyleneisophthalamide). Polymer is prepared in a 2-liter flask equipped withstirrer, condenser and dropping funnel. A charge of 7.32 parts of4-methyl meta-phenylene diamine, 11.1 parts of triethylaminehydrochloride, 12.3 parts of triethylamine and 430 parts of methylenechloride is placed in the flask. A solution of 12.2 parts ofisophthaloyl chloride in 500 parts of methylene chloride is added over aperiod of about 10 seconds. Moderate stirring is continued for threeminutes after which additional portions of each reactant, i.e., (a) 7.32parts of the diamine and 12.3 parts of triethylamine in 322 parts ofmethylene chloride and (b) 12.2 parts of the acid chloride in 322 partsof methylene chloride, are added simultaneously over a period of about30 seconds. After 10 minutes, alpha polymer having an inherent viscosityof 2.03 is obtained. In a similar preparation of the same polymer, theproduct, with an inherent viscosity of 1.38, is observed to have apolymer melt temperature of 330 C.

Example 10 A solution of 6.1 parts of isophthaloyl chloride in 200 partsof methylene chloride is added to a Waring Blendor simultaneously with asolution of 6.33 parts of 4-methoxymetaphenylenediaminemonohydrochloride and 12.1

parts of triethylamine in 200 parts of methylene chloride.

Example 11 2554 parts of 4,6-diamino meta-xylene and 3.975 parts ofsodium carbonate are dissolved in 100 parts of water. A separatesolution of 3.807 parts of isophthaloyl chloride in 136 parts of2,4-dimethy1 tetramethylene sulfone is prepared. The diamine solution isplaced in a Waring Blendor and is agitated rapidly. The acid chloridesolution is then added and stirring is continued for minutes. Thereaction takes place at room temperature, and at the end of the reactiontime the or polymer is precipitated by the addition of Water. Filteredand washed polymer is obtained in a yield which is 100% of theoretical,and the ploymer has an inherent viscosity of 0.81. In a similarpreparation of the same polymer, the product, with an inherent viscosityof 0.92 is observed to have a polymer melt temperature of at least 375C. since it neither softened nor stuck to the heated bar at or belowthat temperature.

Example 12 A copolymer of a MPD-I having an inherent viscosity of 1.45and soluble in dimethylformamide, dimethylacet amide, and in N-methylpyrrolidone is prepared by simultaneously adding to a Waring Blendor asolution of 6.1

parts of isophthaloyl chloride in 150 parts of methylene Example 13 Acopolymer of a MPD-I having an inherent viscosity of 2.08 is preparedfollowing the technique of Example 12 using as one reactant solution4.05 parts of metaphenylene diamine and 7.95 parts of sodium carbonatein 113 parts of water and as the other reactant solution 6.53 parts ofisophthaloyl chloride and 1.15 parts of terephthaloyl chloride in partsof tetrahydrofuran as the other solution. The a MPD-I product contains15% by weight of the copolymeric terephthaloyl repeating unit.

An a MPD-I containing 10% by weight copolymeric terephthaloyl repeatingunit is formed by employing as the second reactant solution in the aboveprocess 6.91 parts of isophthaloyl chloride and 0.77 part terephthaloylchloride in 135 part of tetrahydrofuran. The product has an inherentviscosity of 1.73.

In the preparation of spinning solutions, it is sometimes found thatcarbon dioxide gas is dissolved in the solution. This condition may bedue to the use of a carbonate salt as an acid acceptor duringpolymerization treatment, such as described in US. Patent No. 3,063,966,by Kwolek, Morga and Sorenson, dated November 13, 1962, disclosingpolymerization of wholly aromatic polyamides or, for example, may be acontaminant picked up by contact with the air. The presence of dissolvedcarbon dioxide in solutions to be spun into filaments and the like isundesirable because it frequently tends to cause formation of voids inthe solid filaments. This situation can be remedied by the addition of asmall amount of calcium oxide to the spinning solution. The calciumoxide reacts with carbon dioxide to form calcium carbonate which in thesmall quantities usually encountered is not detrimental in any way tothe spinning solution. Other equivalent chemicals, such as barium oxideor magnesium oxide, as well as bases such as calcium hydroxide, can alsobe used. If desired, the spinning solution Which has been so treatedwith excess calcium oxide can then be carefully neutralized withhydrochloric acid to form soluble calcium chloride.

In the preparation of spinning solutions as discussed above, it issometimes desirable to remove a by-product halogen acid with an hydrousammonia. This process results in the formation of ammonium chloridewhich is then removed by filtration. However, the filtration stepsometimes leaves a turbid solution because of the presence of smallamounts of very finely divided insoluble ammonium chloride. Thisturbidity can be removed by treating the spinning solution with anexcess of propylene oxide which reacts with the ammonium chloride andconverts it to soluble products. The exact nature of these products hasnot been observed, but the reaction occurs rapidly and leads to greaterease in the subsequent spinning operations.

As previously discussed and exemplified, after formation of an organicsolvent solution of the a form of polymer, the shaped form must beprovided by spinning, extrusion, casting or the like, prior totransformation to the 5 form. Care must be taken to avoid increasing thechain mobility or ordering the chain molecules before shaping iscomplete in those cases where no complexing salt is used to solubilizethe beta form. Most conveniently, the transformation to the beta form isaccomplished by application of heat in the presence of air. The periodnecessary for this transformation will vary to some extent dependingupon substituents which may be upon either the meta-phenylene diaminecomponent or the isophthaloyl component of the repeating unit and uponthe liquid in which the shaped structure of polymer is boiled. Table IVshows typical periods of time on the steam bath required to transformvarious or derivatives to the ,8 form in dimethylformamide (except asnoted). Several examples also include water as indicated. Every item wasoriginally soluble in the solvent in which it was heated. The ,8 form ofpolymer which precipitated in the period indicated could in eachinstance be redissolved in the original solvent on addition of lithiumchloride as a complexing salt.

TABLE IV Item MPD Substituonts I Amount Period Water, (min) Percent aNone 1 b None 60 e- 10 5 d 2,4-dimethy1 120 e. 4,6-dimethyl None 1, 440t 2,4,6-trimethyl- None 01%.. None 120 None 120 240 5 240 None 2405-nitro None 10 N-dimethylsulfonamide. None 120 1 Dimethylacetamide usedas solvent.

Rapid transformation frequently occurs at the boiling point of water asseen, and thus the step of transformation to the (3 form may be combinedwith aqueous purification to remove impurities such as salt formed inthe polymerization reaction and/or complexing salt where such was used.The period of the boil-ofi may vary and while transformation to the Bform occurs substantially instantaneously, a more extended washing ispreferred in order to remove residual salts. Generally it is desirablethat the final structure contain no more than about 0.5 to 0.7% byweight of the salt employed in complexing and/ or formed in thereaction. Preferably the salt is reduced to a level which analyzes lessthan about 0.0028 gram atoms anion per 100 grams of fiber, using aboiling solution of equal parts of water and dimethylf-ormamide or aflowing stream of deionized water at a temperature approaching theboiling point.

Prolonged heating of the [3 form of polymer at temperatures above 300 C.(approaching the fusion temperature of the polymer) will causetransformation to the truly cross-linked type of polymer which isinsoluble in concentrated sulfuric acid and which will not form asoluble salt complex in the organic solvents as taught previously.Attempts to form the polymer in a fiberforrning molecular weight rangeby melt polymerization leads to the production of the truly cross-linkedform. Example 14 illustrates such a procedure.

Example 14 A mixture of 5.45 grams of metaphenylene diamine, 8.27 gramsof isophthalic acid and 0.046 gram of p-toluene sulfonic acid are addedto a 55 ml. polymer tube following the technique of Example 6 of US.Patent 2,244,192 to P. I. Flory. The tube is evacuated three times andfilled with dry nitrogen each time. It is then sealed under nitrogenpressure and heated for one hour at 226 C. During this heating periodthe mixture becomes a semi-solid and flows to the bottom of the tube,then slowly changes color from white to yellow to reddish-brown. Littlefurther change is observable after the first half hour of heating. Atthe end of this time the tube is cooled, the seal is broken, and thedistillation head is sealed on. Nitrogen is passed above the polymerwhile it is heated in turn for one hour at 218 C. (using a naphthalenevapor bath), 255 C. (using a diphenyl vapor bath), and 287 C. (using adiphenylene oxide vapor bath). The polymer does not undergo any visiblechange and remains solid during these heating periods. About 1-2 cc. ofa liquid, presumably water, distills from the reaction mixture. Finally,the reaction mixture is heated at 287 C. for three hours at a pressureof 1 mm., then cooled. The contents consist of a red-brown, brittlepolymeric mass, weight 11.95 g.theory for complete amidation topoly-m-phenyleneisophthalamide 11.94 g. The polymer is ground in amortar and characterized as to solubility, X-ray diffraction pattern,and infrared spectrum. Both the infrared spectrum and the X-raydiffraction pattern show that this poylmer is essentially poly-(m-phenyleneisophthalamide). There are slight difierences in theinfrared spectrum which may be due to more end groups in a lowermolecular weight polymer and to groups contributing to cross-linking.The X-ray diffraction pattern shows that this polymer is very highlycrystalline with very good perfection, resembling the beta form of theuncross-linked polymer. The polymer is insoluble in both lithiumchloride-dimethylformamide mixtures (5/ and in concentrated sulfuricacid, thus distinguishing it from the polymers of this invention.

The 5 form of polymer of the present invention is not a cross-linkedstructure since it is possible to convert the a (relatively insoluble)form, to the or (relatively soluble) form. Such conversion isdemonstrated in Example 15 below.

Example 15 Drawn B MPD-I yarn spun from a dimethylformamide solutionessentially as taught in Example 7a is crystallized at high temperatureby the procedure of U.S.P. 3,133,138 and cut to A" staple. Five grams ofthe staple is added to 95 grams of dimethyl acetamide and the mixture ismaintained at 75 C. for three days without eifecting solution. Anotherfive-gram sample of the same fiber is added to 95 grams of dimethylacetamide containing 4% by weight lithium chloride. The fiber dissolvescompletely in three hours, at 75C., without stirring, due to formationof the salt complex.

The salt complex is then destroyed by rapidly adding the solution to alarge volume of water while stirring rapidly in a high-shear blender.Polymer in the or form precipitates. The polymer crumbs so formed arethen washed several times in the blender with additional quantities ofwater and dried at 50C. under vacuum. When five grams of this polymer isadded to 95 gms. dimethyl a-cetamide at room temperature, completesolution is effected within 15 minutes without stirring.

Example 16 This example illustrates the continuous polymerization ofmetaphenylene diamine and isophthaloyl chloride.

Referring to FIGURE V, a solution of 1 part metaphenylene diamine in9.71 parts dimethylacetamide from the diamine source is metered througha cooler to a mixer, into which 1.88 parts of molten isophthaloylchloride from the acid chloride source is simultaneously metered. Themixer is so proportioned and the combined flow of reagents is soselected as to result in turbulent mixing. The molten isophthaloylchloride is fed at 60 C. and the metaphenylene diamine is cooled to l5C. Heat of reaction results in a temperature of 74 C. in the mixerefiiuent which is introduced directly into jacketed, scraped-wall heatexchanger. The heat exchanger has a length to diameter ratio of 32 andis proportioned to have a hold-up of 9.3 minutes. During passage throughthe heat exchanger, the solution temperature is reduced to 29 C. by useof jacket cooling, and continuing polymerization results in an increasein solution viscosity from about 2 poises, as measured at the mixerefiluent, to about 1500 poises, as measured at the heat exchangereffluent. Heat exchanger efiiuent flows continuously to the neutralizer,to which is added continuously 0.311 lb. of calcium hydroxide for eachpound of polymer in the solution. The neutralized solution is thenblended, deaerated, filtered and stored for use in spinning. The finalsolution contains about 20% polymer of 1.65 inherent viscosity and about9.3 calcium chloride.

Polymers of this invention are characterized by an exceptionally highmelting point. Whereas known polyamides melt at temperatures below about270 0., generally the polyamides of this invention in the 18 form havemelting points in excess of 300 C. and in many instances above 350 C.Moreover, filaments of polyamides of this invention retain theirfilament form at temperatures of about 300 C. Polymers of this inventionare also distinguished from known polyamides in having water-whitecolor, excellent resistance to corrosive atmospheres, substantially noflammability. These polymers resist melting upon exposure to 300 C. forextended periods while retaining hitherto unrealized high proportion ofroom temperature physical properties. Flash exposure for 20 seconds totemperatures as high as 700 C. does not destroy these fiber properties.Because of their solubility, these polymers may be processed into shapedstructures such as films and filaments by conventional techniques. Thesepolymers have high tenacity, good work recovery, high flex life atelevated temperatures, and are readily crystallizable.

The polymers of this invention find application in a wide variety ofphysical shapes and forms. Among the most significant of these forms arefibers and films. The useful combination of desirable physical andchemical characteristics of these polymers are unique. Fibers and filmsof these polymers not only possess excellent physical properties at roomtemperatures, but retain their strength and excellent response towork-loading at elevated temperatures for prolonged periods of time.

For many end uses it is satisfactory to employ either amorphous orcrystalline fibers or films. This is particularly true when the end usein mind takes chief advantage of the high melting point and chemicalstability of these polymers. Some end uses require high tenacity atnormal temperatures and resistance to melting under exposure to hightemperatures for short periods of time or even extended periods of time,followed by additional tensioning at lower temperatures. For these, itis found that both amorphous and crystalline fibers are suitable.However, under circumstances which require retention of outstandingphysical properties such as high tenacity and high work recovery whilethe material is subjected to temperatures close to the melting point anddimensional stability under conditions of cyclic change in moisture ortemperature or both in the environment, it is found to be preferablethat the fibers and films of the present invention be in a crystallinestate. Crystalline fibers and films of the polymers of the presentinvention are outstanding in their retention of tenacity at elevatedtemperatures and in their constancy of elongation-to-break underextremely high temperatures. Crystalline fibers, films, and fabrics madefrom crystalline fibers are also more resistant to dimensional shrinkageunder conditions of cyclic wet and hot dry treatment.

The fibers and films of the present invention as normally produced areoriented by drawing or stretching. Fibers are oriented in one direction.Films can be oriented in one or two directions, Following theorientation process, it is possible and sometimes highly desirable,depending upon the end use for which the shaped article is to beemployed, to crystallize the material and to increase thereby itsstability under certain ambient conditions. Of course, as alreadyindicated, the polymer can be crystallized prior to forming into fibers,films and the like, but it is difiicult to retain this crystallinity inthe polymer through the process of spinning a fiber or casting a film.Therefore, it is normally desired to retain the polymer in the amorphouscondition until it has been shaped into a fiber, film, or similararticle and then, as needed, to orient this article and follow theorientation treatment with a crystallization step. There are severalcrystallization treatments known by which the shaped article can becrystallized while retaining the shape and orientation of the product,as shown in some of the examples.

In fiber form the polymers of this invention may be used for hightemperature heat and electrical insulation, protective clothing andcurtains, filtration media, packing and gaske-ting materials, brakelinings and clutch facings. In the aircraft industry these materials canbe used in parachutes, fuel cells, tires, ducts, hoses and insulation.Cordage for tires and conveyor belts, particularly where such materialswould be subject to prolonged high temperature exposure is anotherapplication. Press cloths in the dry cleaning industry prepared fromsuch fibers have extreme hydrolytic stability. In the form of films,these polymers may be used in automotive and aviation interior headlining materials, decorative trim, high temperature heat and electricalinsulation, such as for slot liners, use in dry transformers,capacitors, cable wrap pings, etc., packaging of items to be exposed tohigh temperature while Within the package, corrosion resistant pipe, hotwater pipe, duct work, hot air ventilation, aircraft body skins,aircraft radomes, embossing roll covers, containers and containerlinings, printed circuits, tape for hot pipe overwrapping, laminatedstructures where the films are bonded to metal sheets or foils, moldliners or self-sustaining containers for casting low-melting (below 300C.) fusible materials, including metals, and a variety of other similarand related uses. Valuable flexible materials similar in function toputty with outstanding high temperature stability can be made bycombining fibers prepared from polymers of the present invention withflexible high-temperature polymers such as plasticizedchlorotrifluoroethylene polymers.

Films formed from polymers of this invention may be stretched orotherwise oriented according to conventional procedures. Films may beoriented biaxiall by stretching or rolling in both directions or byrolling in one direction and stretching in the other.

Because they retain fiber properties at elevated temperatures, fibersfrom the polymers of this invention can be used in high temperatureapplications along with heatresistant resins and elastomers, such aspolytetrafiuoroethylene, fluoroethylene, fluoro-rubbers and siliconeresins. Fabrics from aromatic polyamide fibers form a base material towhich resins can be applied as a coating or impregnant, also, staplefibers can be mixed into a matrice of the resin to give a reinforcedplastic material. Since these fibers melt at temperatures higher thansome resins do, resins can be applied to them in molten form, or can besintered after application as a solid powder, without damage to thefibers. Moreover, since the fibers retain good tensile properties athigh temperatures, resins can be applied to the fabric ina continuousmanner, its high strength permitting the fabric to be processed, e.g.,run through a sintering furnace, without any need for supportingmembers. The products so obtained can be used at much highertemperatures than is possible with conventional fibers which decomposeor melt below 300 C.

Solutions of polymers of this invention are valuable as varnishes,adhesives, wire-coatings, fabric-coatings, and

similar products. Fabrics suitable as a substrate for the Manyequivalent modifications will be apparent to those skilled in the artwithout a departure from the inventive concept.

What is claimed is:

1. Polycarbonarnide having an inherent viscosity of at least 0.8 insulfuric acid at 30 C. at a concentration of 0.5 gram of polymer per 100cc. of solution, the said polycarbonamide being of the class consistingof (a) an alpha polymetaphenylene isophthalamide characterized byrelatively high solubility and (b) a beta polymetaphenyleneisophthalamide characterized by relatively low solubility, the saidpolycarbonamide consisting of repeating units of which at least about85% are of the formula wherein the hexagon represents the benzenenucleus, R is a substituent which is non-amide forming at roomtemperature via reaction with a member from the class consist'ing ofamino hydrogen and carbonyl halide.

2. Polycarbonarnide having an inherent viscosity of at least 0.8 insulfuric acid at 30 C. at a concentration of 0.5 gram of polymer per 100cc. of solution, the said polycarbonamide being of the class consistingof (a) an alpha polymetaphenylene isophthalamide characterized byrelatively high solubility and (b) a beta polymetaphenyleneisophthalamide characterized by relatively low solubility, the saidpolycarbonamide consisting of repeating units of which at least about85% are of the formula wherein the hexagon represents the benzenenucleus, R is a substituent on nuclear carbon from the class consistingof hydrogen, lower alkyl, lower alkoxy, halogen, nitro, cyano, sulfo andlower carbalkoxy.

3. The polycarbonamide of claim 2 wherein at least two R substituentsare hydrogen and copolymeric units when present are carbonamidic.

4. Polycarbonamide having an inherent viscosity of at least 0.8 insulfuric acid of 30 C. at a concentration of 0.5 gram of polymer per 100cc., the said polycarbonl t: amide being an alpha polymetaphenyleneisophthalamide characterized by relatively high solubility andconsisting of repeating units of which at least about 85% are of theformula wherein the hexagon represents the benzene nucleus, R is asubstituent on nuclear carbon from the class consisting of hydrogen,lower alkyl, lower alkoxy, halogen, nitro, cyano, sulfo and lowercarbalkoxy, at least three of the said R substitutents being hydrogen.

5. Polycarbonamide havingan inherent viscosity of at least 0.8 insulfuric acid at 30 C. at a concentration of 0.5 gram of polymer per 100cc. of solution, the said polycarbonamide being a beta polymetaphenyleneisophthalamide characterized by relatively low solubility and consistingof repeating units of which at least about 85% are of the. formulawherein the hexagon represents the benzene nucleus, R is a substituenton nuclear carbon from the class consisting of hydrogen, lower alkyl,lower alkoxy, halogen, nitro, cyano, sulfo and lower carbalkoxy, atleast three of the said R substituents being hydrogen.

6. A fiber of the polymer of claim 2.

7. A film of the polymer of claim 2.

8; A fiber of polymetaphenylene isophthalamide. 9. A film ofpolymetaphenylene isophthalamide.

References Cited by the Examiner UNITED STATES PATENTS 2,244,192 6/ 1941Flory 2.60-78 2,625,536 1/1953 Kirby 26078 2,831,834 4/1958 Magat 260-78WILLIAM H. SHORT, Primary Examiner.

H. D. ANDERSON, Assistant Examiner.

1. POLYCARBONAMIDE HAVING AN INHERENT VISCOSITY OF AT LEAST 0.8 IN SULFURIC ACID AT 30*C. AT A CONCENTRATION OF 0.5 GRAM OF POLYMER PER 100 CC. OF SOLUTION, THE SAID POLYCARBONAMIDE BEING OF THE CLASS CONSISTING OF (A) AN ALPHA POLYMETAPHENYLENE ISOPHTHALAMIDE CHARACTERIZED BY RELATIVELY HIGH SOLUBILITY AND (B) A BETA POLYMETAPHENYLENE ISOPHTHALAMIDE CHARACTERIZED BY RELATIVELY LOW SOLUBILITY, THE SAID POLYCARBONAMIDE CONTAINING OF REPEATING UNITS OF WHICH AT LEAST ABOUT 85% ARE OF THE FORMULA 